With the discovery of high temperature superconductivity in copper oxides as a turning point, perovskite-type oxides including various types of transition metals have been drawing attention, and diligent research has been conducted. In addition, the discovery of colossal magneto-resistance (hereinafter referred to as CMR) effects, where change in electrical resistivity spans over many digits as a phenomenon of a type of magnetic field melting of a charge ordered phase in a perovskite-type Mn oxide in the continuing process of design and development of related substances has spurred more and more research.
In addition, colossal electro-resistance (hereinafter referred to as CER) changing effects, which is a phenomenon similar to CMR in perovskite-type transition metal oxides, such as Pr0.7Ca0.3MnO3, induced through application of an electrical field or current, were discovered, and a memory element using CER effects is introduced in Patent Document 1.
Patent Document 2 introduces a nonvolatile memory element having a structure where a perovskite-type transition metal oxide exhibiting CER effects as Pr0.7Ca0.3MnO3, is used for a semiconductor switch layer, and this semiconductor switch layer is sandwiched between metal electrodes. A resistance random access memory (hereinafter referred to as RRAM) formed of nonvolatile memory elements using this perovskite-type transition metal oxide is characterized by high speed operation, low power consumption, nondestructive readout and the like, in addition to nonvolatile properties, and therefore, expected to substitute DRAM's, SRAM's and flash memories as a universal memory, and thus, development thereof has been progressing.
In recent years, it has been reported that CER effects occur at the interface between a perovskite-type oxide and another metal material. As perovskite-type Mn oxides exhibiting such CER effects, a large number of materials, for example Pr1-xCaxMnO3, Pr1-x(Ca, Sr)xMnO3 and Nd0.5Sr0.5MnO3, are known. In addition, perovskite-type copper oxides, such as Bi2Sr2CaCu2O8+y, RuSr2GdCu2O3 and the like are known. Furthermore, a great number of nonvolatile memories, for example, of the 1T1R type, where CER effects gained by the above described oxides are controlled by a current or an electrical field have been proposed.
It has been reported that electrical conductive properties, including CER effects of the above described perovskite-type Mn oxides and copper oxides, which are intensely correlated electron materials, change greatly due to changes in the concentration of charge and changes in the crystal structure caused by slight changes in the composition. Therefore, it is necessary to control precisely the composition of the perovskite-type Mn-oxide and the copper-oxide material thin films, in order to secure uniformity and reproducibility for the element operation properties when a nonvolatile memory element where CER effects are controlled by a current or an electrical field is fabricated.
The above described perovskite-type Mn oxides and copper oxides, however, are compounds formed of four or more elements, and therefore, there is a drawback, such that it is difficult to control the composition when a thin film is fabricated for an element.    Patent Document 1: Japanese Unexamined Patent Publication No. H10 (1998)-255481    Patent Document 2: Japanese Unexamined Patent Publication No. 2003-338607    Patent Document 3: Japanese Unexamined Patent Publication No. 2004-119958    Non-Patent Document 1: Physica C Vol. 366, p. 23 (2001)    Non-Patent Document 2: Appl. Phys. Lett. Vol. 83, No. 5, p. 957 (2003)    Non-Patent Document 3: Appl. Phys. Lett. Vol. 85, No. 12, p. 317 (2004)